+1 -- at the very least, this strikes me as an exciting and provocative
new angle from which to look at the value / reference / subtype /
pattern matching problem space that's been discussed on this list.
On 4 May 2016, at 15:25, Matthew Johnson via swift-evolution wrote:
On May 4, 2016, at 4:46 PM, Austin Zheng via swift-evolution
<[email protected]> wrote:
Hello swift-evolution:
Based on recent conversations on the list, I'd like to float a trial
balloon: an "enum class" kind which is analogous to classes in the
same way existing enums are to structs. This is a data type which
allows the user to define a number of cases, like enums, and can
participate in pattern matching and exhaustivity analysis. Instances
of an enum class are reference types, which enables (for example)
graph nodes with a built-in concept of identity.
To be slightly more fanciful, perhaps such a kind could be treated as
an 'almost-final' class, with each case being a nested type which is
defined as a final subclass of the enum class. Cases could then
define their own behavior:
enum class GraphNode {
case Node(left: GraphNode, right: GraphNode) {
override func foo() { ... }
func nodeSpecificMethod() { ... }
}
case Leaf {
override func foo() { ... }
func leafSpecificMethod() { ... }
}
func foo() { ... }
}
let x : GraphNode = GraphNode.newEmptyTree()
let y : GraphNode = GraphNode.Node(l, r)
let z : GraphNode = GraphNode.Leaf()
let a : GraphNode.Leaf = GraphNode.Leaf()
Enum classes would not be subclassible, and extensions would not be
able to define new cases (as is the case with normal enums at the
present time).
My superficial analysis seems to suggest that this would solve two
issues: providing a reference-semantics type with all the pattern
matching functionality of current enums, and providing a construct
for modeling case-class style ADTs where each case should be treated
as a subtype (as has been occasionally proposed).
I would like feedback as to:
- Whether this is something that would be useful enough to justify
additional language features
- Whether this is something that would be theoretically well-founded
and elegant
This is definitely an idea worth exploring. I am interested in
hearing from folks who have experience with Scala case classes. How
have you found them useful in ways that Swift’s current enums do not
address?
Thanks for your time, and have a great day!
Austin
_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
